Heretofore, when the vacuum chamber of a film forming apparatus in which dust in large quantity may be generated is, for example, evacuated by a vacuum pump, it is known that there is provided a mesh member for adhering or collecting the dusts in a gas to be evacuated, the mesh member being interposed in an evacuating passage to protect the vacuum pump from the dusts. It is also known that a drum rotating in oil is provided in the evacuating passage to adhere the dusts in the gas to be evacuated to the surface of the drum or small articles which are contained in the drum.
In an ultrafine particle producing apparatus, produced ultrafine particles are deposited in a collecting chamber to be collected.
When the gas to be evacuated is passed through the mesh member or the drum rotating in oil, Reynolds number is small since the evacuated gas is lower pressure, and the flow is laminar. Therefore, the above-mentioned adhesion of fine or ultrafine particles mainly depends on the diffusion effect by the Brownian motion of these particles.
In this case, in order to sufficiently remove the dusts, it is necessary to narrow the evacuating passage through which the evacuated gas is flowed, and therefore a large difference in pressure is required to pass the evacuated gas. This pressure difference has disadvantage that it causes the pressure in the vacuum chamber of the film forming apparatus to be raisen. Thus, the evacuating passage should be formed relatively large so as not to considerably increase the pressure difference, and this makes it difficult to sufficiently remove the dusts from the evacuated gas. Since there is the pressure difference between the vacuum chamber and the evacuating system, the vacuum pump which is to be used for evacuating the vacuum chamber is limited to a low (rough) vacuum type, and there is a disadvantage that a high vacuum condition can not be obtained in the vacuum chamber. Further, with using of oil to remove the dusts, oil component may flow into the vacuum chamber, which unpreferably gives adverse influence to the film forming apparatus.
With the ultrafine particle producing apparatus, the produced ultrafine particles are intaken together with the evacuated gas by the vacuum pump to cause defects to deteriorate the efficiency for collecting these particles.
It is, therefore, an object of the present invention to solve the drawbacks of the above-mentioned conventional apparatuses and to provide a fine particle collector arrangement for vacuum pumps which can effectively collect fine particles such as dusts or the like in low pressure gas without raising the pressure difference between a vacuum chamber and an evacuating system.
Another object of the invention is to provide a fine particle collector arrangement for vacuum pumps which makes it possible to use a vacuum pump obtaining relatively high vacuum with ready manufacture and provide easy maintenance.
A further object of the invention is to provide a fine particle collector arrangement for vacuum pumps which may be utilized for collecting ultrafine particles produced in an ultrafine particle producing apparatus.